The present invention is directed to antimicrobial compositions containing active ingredients which are oligomers and/or polymers of xcex2-amino acids.
Chemists have long sought to extrapolate the power of biological catalysis and recognition to synthetic systems. These efforts have focused largely on low molecular weight catalysts and receptors. Most biological systems, however, rely almost exclusively on large polymers such as proteins and RNA to perform complex chemical functions.
Proteins and RNA are unique in their ability to adopt compact, well-ordered conformations. These two biopolymers are unique also because they can perform complex chemical operations (e.g., catalysis, highly selective recognition, etc.). Folding is linked to function in both proteins and RNA because the creation of an xe2x80x9cactive sitexe2x80x9d requires proper positioning of reactive groups. Consequently, there has been a long-felt need to identify synthetic polymer backbones which display discrete and predictable folding propensities (hereinafter referred to as xe2x80x9cfoldamersxe2x80x9d) to mimic natural biological systems. Such backbones will provide molecular xe2x80x9ctoolsxe2x80x9d to probe the functionality of large-molecule interactions (e.g. protein-protein and protein-RNA interactions).
Much work on xcex2-amino acids and peptides synthesized therefrom has been performed by a group led by Dieter Seebach in Zurich, Switzerland. See, for example, Seebach et al. (1996) Helv. Chim. Acta. 79:913-941; and Seebach et al. (1996) Helv. Chim. Acta. 79:2043-2066. In the first of these two papers Seebach et al. describe the synthesis and characterization of a xcex2-hexapeptide, namely (H-xcex2-HVal-xcex2-HAla-xcex2-HLeu)2-OH. Interestingly, this paper specifically notes that prior art reports on the structure of xcex2-peptides have been contradictory and xe2x80x9cpartially controversial.xe2x80x9d In the second paper, Seebach et al. explore the secondary structure of the above-noted xcex2-hexapeptide and the effects of residue variation on the secondary structure.
Dado and Gellman (1994) J. Am. Chem. Soc. 116:1054-1062 describe intramolecular hydrogen bonding in derivatives of xcex2-alanine and xcex3-amino butyric acid. This paper postulates that xcex2-peptides will fold in manners similar to xcex1-amino acid polymers if intramolecular hydrogen bonding between nearest neighbor amide groups on the polymer backbone is not favored.
Suhara et al. (1996) Tetrahedron Lett. 37(10):1575-1578 report a polysaccharide analog of a xcex2-peptide in which D-glycocylamine derivatives are linked to each other via a C-1 xcex2-carboxylate and a C-2 xcex1-amino group. This class of compounds has been given the trivial name xe2x80x9ccarbopeptoids.xe2x80x9d
Hamuro et al. (1999) J. Am. Chem. Soc. 121:12200-12201, describe antibacterial compositions containing xcex2-peptides having a repeating 3-peptide residue motif. The compounds described are: Fmoc-(xcex23-HVal-xcex23-HLys-xcex23-HLeu)n-OH (n=2-4); H-(xcex23-HVal-xcex23-HLys-xcex23-HLeu)n-OH (n=2-4); and H-(xcex23-HLeu-xcex23-HLys-xcex23-HLeu)n-OH (n=2-6). While these xcex2-peptides are described as being antibacterial, they are also hemolytic at concentrations near the effective antibacterial concentrations, thus limiting their utility as medicaments.
The increasing prevalence of pathogenic bacteria that are resistant to common chemotherapies has prompted an intensive search for new antibiotics. Cationic peptides that adopt amphiphilic secondary structures (e.g., magainins) constitute a widespread host defense against microbial invasions, and mimicry of these natural antibiotics led the present inventors on a search for new synthetic antimicrobial agents. Many of the cationic antimicrobial peptides appear to act by disrupting bacterial membranes, a mechanism that may not be conducive to the development of resistance. The subject invention is directed to antimicrobial compositions containing unnatural cationic oligomers that have no known natural counterpart and that display antibiotic activity comparable to that of a magainin derivative against at least four different bacterial species, including two pathogens that are resistant to common antibiotics. The oligomers are constructed from xcex2-amino acid building blocks rather than the xcex1-amino acid building blocks of conventional peptides. These xcex2-peptides exhibit lower hemolytic activity than does the magainin derivative, which indicates a favorable selectivity for bacterial cells relative to mammalian cells. Because xcex2-peptides are not expected to be subject to protease degradation, these results point toward the rational design of a promising new antibiotic class.
Specifically, the present invention is directed to compounds and to antimicrobial compositions containing the compounds, that is, compositions which inhibit the growth of microbes in general and bacteria and fungi in particular, the compositions comprising an antimicrobial-effective amount of a xcex2-amino acid oligomer or polymer of the formula:
W-(xe2x80xa2xe2x80xa2xe2x80xa2-A-B-C-xe2x80xa2xe2x80xa2xe2x80xa2)-Z
wherein xe2x80x9cxe2x80xa2xe2x80xa2xe2x80xa2-A-B-C-xe2x80xa2xe2x80xa2xe2x80xa2xe2x80x9d represents a xcex2-amino acid oligomer or polymer chain, each of A, B, C, etc. representing individual residues of the oligomer or polymer chain and the ellipses representing adjacent N-terminal and C-terminal xcex2-amino acid residues of the same genus, wherein each residue of the oligomer or polymer chain (that is, each A, B, C, etc.) is the same or different and is independently selected from the group consisting of: 
wherein X is selected from the group consisting of hydrogen, linear or branched C1-C6-alkyl, alkenyl, or alkynyl; mono- or bicyclic aryl, mono- or bicyclic heteroaryl having up to 5 heteroatoms selected from N, O, and S; mono- or bicyclic aryl-C1-C6-alkyl, mono- or bicyclic heteroaryl-C1-C6-alkyl, xe2x80x94(CH2)n+1xe2x80x94OR, xe2x80x94(CH2)n+1xe2x80x94SR, xe2x80x94(CH2)n+1xe2x80x94S(xe2x95x90O)xe2x80x94CH2xe2x80x94R, xe2x80x94(CH2)n+1xe2x80x94S(xe2x95x90O)2xe2x80x94CH2xe2x80x94R, xe2x80x94(CH2)n+1xe2x80x94NRR, xe2x80x94(CH2)n+1xe2x80x94NHC(xe2x95x90O)R, xe2x80x94(CH2)n+1xe2x80x94NHS(xe2x95x90O)2xe2x80x94CH2xe2x80x94R, xe2x80x94(CH2)n+1xe2x80x94Oxe2x80x94(CH)mxe2x80x94R1, xe2x80x94(CH2)n+1xe2x80x94Sxe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)n+1xe2x80x94S(xe2x95x90O)xe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)n+1xe2x80x94S(xe2x95x90O)2xe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)n+1xe2x80x94NHxe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)n+1xe2x80x94Nxe2x80x94{(CH2)mxe2x80x94R1}2, xe2x80x94(CH2)n+1xe2x80x94NHC(xe2x95x90O)xe2x80x94(CH2)n+1xe2x80x94R1, and xe2x80x94(CH2)n+1xe2x80x94NHS(xe2x95x90O)2xe2x80x94(CH2)mxe2x80x94R1;
wherein R is independently selected from the group consisting of hydrogen, C1-C6-alkyl, alkenyl, or alkynyl; mono- or bicyclic aryl, mono- or bicyclic heteraryl having up to 5 heteroatoms selected from N, O, and S; mono- or bicyclic aryl-C1-C6-alkyl, mono- or bicyclic heteroaryl-C1-C6-alkyl; and
wherein R1 is selected from the group consisting of hydroxy, C1-C6-alkyloxy, aryloxy, heteroaryloxy, thio, C1-C6-alkylthio, C1-C6-alkylsulfinyl, C1-C6-alkylsulfonyl, arylthio, arylsulfinyl, arylsulfonyl, heteroarylthio, heteroarylsulfinyl, heteroarylsulfonyl, amino, mono- or di-C1-C6-alkylamino, mono- or diarylamino, mono- or diheteroarylamino, N-alkyl-N-arylamino, N-alkyl-N-heteroarylamino, N-aryl-N-heteroarylamino, aryl-C1-C6-alkylamino, carboxylic acid, carboxamide, mono- or di-C1-C6-alkylcarboxamide, mono- or diarylcarboxamide, mono- or diheteroarylcarboxamide, N-alkyl-N-arylcarboxamide, N-alkyl-N-heteroarylcarboxamide, N-aryl-N-heteroarylcarboxamide, sulfonic acid, sulfonamide, mono- or di-C1-C6-alkylsulfonamide, mono- or diarylsulfonamide, mono- or diheteroarylsulfonamide, N-alkyl-N-arylsulfonamide, N-alkyl-N-heteroarylsulfonamide, N-aryl-N-heteroarylsulfonamide, urea; mono- di- or tri-substituted urea, wherein the subsitutent(s) is selected from the group consisting of C1-C6-alkyl, aryl, heteroaryl; O-alkylurethane, O-arylurethane, and O-heteroarylurethane;
wherein Y is selected from the group consisting of hydrogen, linear or branched C1-C6-alkyl, alkenyl, or alkynyl; mono- or bicyclic aryl, mono- or bicyclic heteroaryl having up to 5 heteroatoms selected from N, O, and S; mono- or bicyclic aryl-C1-C6-alkyl, mono- or bicyclic heteroaryl-C1-C6-alkyl, xe2x80x94(CH2)nxe2x80x94OR, xe2x80x94(CH2)nxe2x80x94SR, xe2x80x94(CH2)nxe2x80x94S(xe2x95x90O)xe2x80x94CH2xe2x80x94R, xe2x80x94(CH2)nxe2x80x94S(xe2x95x90O)2xe2x80x94CH2xe2x80x94R, xe2x80x94(CH2)nxe2x80x94NRR, xe2x80x94(CH2)nxe2x80x94NHC(xe2x95x90O)R, xe2x80x94(CH2)nxe2x80x94NHS(xe2x95x90O)2xe2x80x94CH2xe2x80x94R, xe2x80x94(CH2)nxe2x80x94Oxe2x80x94(CH)mxe2x80x94R1, xe2x80x94(CH2)nxe2x80x94Sxe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)nxe2x80x94S(xe2x95x90O)xe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)nxe2x80x94S(xe2x95x90O)2xe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)nxe2x80x94NHxe2x80x94(CH2)mxe2x80x94R1, xe2x80x94(CH2)nxe2x80x94Nxe2x80x94{(CH2)mxe2x80x94R1}2xe2x80x94(CH2)nxe2x80x94NHC(xe2x95x90O)xe2x80x94(CH2)mxe2x80x94R1, and xe2x80x94(CH2)nxe2x80x94NHS(xe2x95x90O)2xe2x80x94(CH2)mxe2x80x94R1;
wherein R and R1 are as defined above; or
X and Y combined, together with the carbon atoms to which they are bonded, independently define a substituted or unsubstituted C3-C8 cycloalkyl, cycloalkenyl or heterocyclic ring having one or more N, O or S atom(s) as the heteroatom(s);
the substituents on carbon atoms of these rings being independently selected from the group consisting of linear or branched C1-C6-alkyl, alkenyl, alkynyl; mono- or bicyclic aryl, mono- or bicyclic heteraryl having up to 5 heteroatoms selected from N, O, and S; mono- or bicyclic aryl-C1-C6-alkyl, mono- or bicyclic heteroaryl-C1-C6-alkyl, and the substituents listed above for X and Y when X and Y are not combined;
the substituents on nitrogen heteroatoms being independently selected from the group consisting of xe2x80x94S(xe2x95x90O)2xe2x80x94CH2xe2x80x94R, xe2x80x94C(xe2x95x90O)xe2x80x94R, xe2x80x94S(xe2x95x90O)2xe2x80x94(CH2)mxe2x80x94R1, xe2x80x94C(xe2x95x90O)xe2x80x94(CH2)n+1xe2x80x94R1; wherein R and R1 are as defined above;
m is an integer of from 2-6 and n is an integer of from 0-6;
W is hydrogen or an amino-terminal capping group (such as formyl, acetyl, tBoc, Fmoc, etc.); Z is hydroxy or a carboxy-terminal capping group (such as NH2, NH(alkyl), N(alkyl)2, etc.); and wherein the total number of residues is greater than 6; and further wherein in at least one residue, X and Y are combined in a cyclic moiety; pharmaceutically-suitable salts thereof, and combinations thereof; optionally in combination with a pharmaceutically-suitable carrier.
When X is not combined with Y, X and Y are preferably (and independently) selected from the group consisting of linear or branched C1-C6-alkyl, hydroxy-C1-C6-alkyl, amino-C1-C6-alkyl, aryl-C1-C6-alkyl, heteroaryl-C1-C6-alkyl, and carboxyl-C1-C6-alkyl. When X and Y are combined together into a cyclic substituent, together X and Y and the carbons to which they are bonded define a substituted or unsubstituted cyclopentyl, substituted or unsubstituted cyclohexyl, unsubstituted or N-substituted piperidinyl, or unsubstituted or N-substituted pyrrolidinyl.
In a another embodiment, the composition contains a xcex2-amino acid oligomer or polymer of the above, wherein each residue (A, B, C, etc.) of the oligomer is a xcex2-amino acid residue of formula: 
wherein X and Y combined, together with the carbon atoms to which they are bonded, independently from residue to residue define a substituted or unsubsituted C3-C8 cycloalkyl, cycloalkenyl or heterocyclic ring having one or more nitrogen atoms as the sole heteroatom, the substituents being selected from the group consisting of hydroxy, linear or branched C1-C6-alkyl, alkenyl, alkynyl; hydroxy-C1-C6-alkyl, amino-C1-C6-alkyl, C1-C6-alkyloxy, C1-C6-alkyloxy-C1-C6-alkyl, amino, mono- or di-C1-C6-alkylamino, carboxamido, carboxamido-C1-C6-alkyl, sulfonamido, sulfonamido-C1-C6-alkyl, urea, cyano, fluoro, thio, C1-C6-alkylthio, mono- or bicyclic aryl, mono- or bicyclic heteraryl having up to 5 heteroatoms selected from N, O, and S; mono- or bicyclic aryl-C1-C6-alkyl, heteroaryl-C1-C6-alkyl, and combinations thereof; where n is a positive integer greater than 6; and pharmaceutically-acceptable salts thereof, optionally in combination with a pharmaceutically-suitable carrier.
The invention is likewise directed to a method of inhibiting microbial growth in mammals, including humans, the method comprising administering an antimicrobial amount of a composition as recited above to a patient in need thereof.
Other aims, objects, and advantages of the invention will appear more fully from a complete reading of the following Detailed Description of the Invention and the attached claims.